Device for optionally switching on either of two filament cathodes of an X-ray tube



Nov. 12, 1963 J. FRANSEN 3,110,810

DEVICE FOR OPTIONALLY SWITCHING ON EITHER OF TWO FILAMENT CATHODES OF AN X-RAY TUBE Filed Oct. 26, 1959 vIvvIIvvv lllll FIG.3

| AAAAAC "vvIvIIIvvv Fl 6.4 lNVENTOR Jclcobus F'ranscn 'AGENT United States Patent 3,110,810 DEVHCE FOR OPTIONALLY SWITCHING ON EITHER OF TWO FILAMENT CATHODES OF AN X-RAY TUBE Jacobus Fransen, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Oct. 26, 1959, Ser. No. 848,813 Claims priority, application Netherlands Oct. 30, 1958 4 Claims. (Cl. 250100) The invention relates to a device for supplying, at will, the filament current to either of two filament wires of an X-ray tube.

It is known that for X-ray fiuoroscopy and radiography the anode load in an X-ray tube may exhibit material differences. In order to maintain the specific load of the anode surface in both cases at approximately the same value, use is made of focal spots of different size. By varying the diameter of the electron beam the size of the focal spot may be varied, but the control required for this purpose cannot be obtained in a simple manner. It is preferred to provide two filament cathodes in the X-ray tube. For other reasons provision may be made of still more cathodes. The focus desired for each of the uses is obtained on the anode surface with the aid of suitable control-means for the electron rays.

The filament cathodes are formed by filament wires which are heated by electric currents up to the temperature at which adequate electron emission is obtained. It is known to provide the envelope, surrounding the X-ray tube for high-voltage screening of live pants, with a switch by which the current can be transferred from one filament wire to the other. This has the advantage that the electric current can be supplied by way of two current conductors, so (that between the tube envelope and the voltage source the conventional twin-core high-voltage cable can always be employed.

It is, however, a disadvantage that switching must take place at the envelope of the tube. All manipulations required for taking a nadiograph or for X-ray fluoroscopy are preferably carried out at the place where the supply set or the associated switching desk are located. The actuation of the switch at the tube envelope reduces the simplicity with which the required manipulations can be carried out. Moreover, the tube envelope must be constructed so that the switch can be actuated from the outer side, which involves a more complicated construction.

The invention has for its object to obviate these disadvantages. iln accordance with the invention one phase of its supply voltage can be switched on for one filament wire, whereas for the other filament wire the other phase of the associated supply voltage can be switched on so that the current passing through the common part of the filament current circuits for one filament wire has a sense opposite that of the current for the other filament wire. The desired current circuit may be closed by means of a switch comprising a movable con-tact, which can be connected to either of two stationary contacts and is connected to the two filament wires by way of rectifiers connected in phase opposition. The stationary contacts are connected to one terminal of the voltage source intended for the filament wires via rectifiers connected in phase opposition. The difference in the currents required for heating may be obtained by connecting a resistor in series with one of the filament wires. In this case one common filament-current transformer for the two filament wires suflices. The two filament wires are connected directly to one terminal of the transformer winding and to the other by way of the rectifiers and the switch. In this case the filament current for the two wires consists of a sequence of half-waves of the alternating current.

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As an alternative, the stationary contacts of the switch may be connected via rectifiers to separate filament current windings, of which the voltages have (the same phase but :diiferent values. Then one end of the two windings is connected to the common supply wire for the two filament wires. If it is preferred not to use half waves, in order to avoid unfavourable loading of one, or in the case of separate current sources, of both the transformer windings, use may be made, in accordance with the invention, of a four-rectifier circuit arrangement comprising a transformer of which the secondary winding has a neutral point. The stationary contacts of the switch may then be connected to the ends of the windings via a fourelenient rectifying circuit and the neutral point to the current conductor which is directly connected to the two filament wires. I t

The invention permits arranging the switch in the supply unit for the X-ray tube or in the associated switching desk so that the correct position of the switch can be chosen simultaneously with the preparation of taking radiographs or for fiuoroscopy. The switching may be performed automatically by means of a control-member by which other manipulations characteristic of the nature of the load to be obtained are accomplished. Errors are thus excluded.

The invention will now be described more fully with reference to the drawing, in which FIGS. 1, 2 and 3 show various switching possibilities in the device according to the invention and FIG. 4 shows diagrammatically an X-ray apparatus, in which the device according to the invention is employed.

The filament wires 1 and 2 of an X-ray tube not shown in FIGS. 1, -2 and 3 must be connectable at will to a suitable voltage to supply the filament current. As shown in FIG. 1, the filament current transformer required to this end is provided with a primary winding 3 and a secondary winding 4. One end of the secondary winding 4 is directly connected by way of the conductor 5 to a connection 6, which connects at the same time the two filaments 1 and 2. The other end of the secondary winding 4 of the filament current transformer is connected by way of the rectifier 7 to a stationary contact 8 of a switch and by way of a second rectifier 9 in phase opposition to a second stationary contact 10 of the same switch. This switch has also a movable contact 11, which can be connected at will to one or to the other of the two stationary contacts. The movable contact is connected to the two filament wires by the conductor 12. This conductor is connected via the rectifier 13 to the filament wire 1 and via the .retcifier 14, connected in phase opposition, to the filament wire 2, in both cases to the ends of these filament Wires which are .not connected to the current conductor 5. The rectifier 14 has connected with it in series the resistor 15. In accordance with the position of the contact arm 11, electric current is passed through one or throughthe other of the filament wires. In the position shown, the filament wire 2 is operative. The rectifiers 7 and 14 allow the current to pass in the same direction. In the opposite phase, in which the rectifier 13 passes current, the rectifier 7 cuts off the current, so that no current is supplied to the filament wire 1. At the change-over of the movable contact into the position shown in broken lines, the current again passes through rectifiers which pass the current in the same direction, i.e. through the rectifiers 9 and 13 and then through the filament wire 1. The current path via the filament wire 2 is thencut off by the rectifier 14.

The resistor 15 serves to restrict the current through the filament Wire 2 to the value required for fluoroscopy, which value is lower than that required for heating the filament wire 1, which is in use when the X-ray tube is employed for making radiographs.

Use is preferably made of dry rectifiers, such as selenium cells or silicon diodes.

A circuit arrangement in which the resistor 15 may be omitted, is shown in FIG. 2. This arrangement differs from that shown in FIG. 1 only in that the filament current transformer has two secondary windings instead of one. These secondary windings supply voltages of the same phase but of different values. At one end the two windings are connected to the current conductor 5. The other end of the winding 16 is connected via the rectifier 9 to the stationary contact ll of the switch. This winding 16 supplies a higher voltage than the winding 17, of which the other end is connected via the rectifier 7 to the stationary contact 8 of the switch.

There may be objections to having only half-wave rectification of the alternating current. This objection may be obviated by means of the arrangement shown in FIG. 3, in which a filament current transformer with a primary winding 3 and a secondary winding 18 is employed. This winding supplies a voltage which has twice the value of the maximum required voltage and is provided with a neutral point 19, which is connected by the current conductor 5 to the connection 6, which connects the two filament wires 1 and 2. The two ends of the winding 18 are connected to a bridge circuit 20 of rectifiers, of which the current tappings are connected each to one of the stationary contacts 8 and 10 of the switch. The movable contact 11 thereof is connected in the manner set forth to the filament wires 1 and 2. The filament Wires are traversed in this case by two-phase rectified current and the transformer is loaded during the two half periods.

FIG. 4 shows an X-ray tube 21, surrounded by a jacket 22. It is common practice to manufacture the jacket of sheet material, and to fill the space between the sheath and the tube with oil. The two filament wires 1 and 2 are shown diagrammatically. The X-ray tube 21 comprises an anode 23, secured to the wall. The X-rays can project through a window 24 in the sheath wall to the outside. By means of insulators 25 and 26 the highvoltage cables 27 and 28 are secured to the sheath. The conductor 29 of the cable 28 is connected to the anode 23.

The two filament wires -1 and 2 are arranged opposite the front surface of the anode 23. The current supply wires are taken through the wall to the outside. The conductor 5, which is connected to the terminal 6 of the two filament wires, leads directly to the cable end 25. In the connection to the other end of the filament wire 1 is included the rectifier 13 and in the connection to the other end of the filament Wire 2 are included the rectifier 14 and the resistor 15. These connections are united in the current conductor 12, which leads to the cable end 25. The cable 27 comprises consequently only the two current conductors 5 and '12.

The cable 27 is secured by means of an insulator 39 for high-voltage and the cable 28 by means of a similar insulator 31 to the wall 32 of the voltage supply source. In a metal housing 32 is housed the high-voltage transformer 33. The conductor 29 is connected to this transformer. The housing 32 includes furthermore the filament current transformer 34. The current conductor 5 is connected both to the filament current transformer 34 and to the high-voltage transformer 33. In the current conductor 12 is included the movable contact 11 of the switch, of which the stationary contacts 8 and 10 are connected via the rectifiers 7 and 9 to the other terminal 35 of the filament current transformer.

For moving the switching arm 11 use may be made of a high-voltage-insulated COHiEI'Ol-tl'l'lflmbfil', which is taken through the wall of the housing 32, so that a control from the outside is possible.

If the further control-members of the X-ray apparatus re collected on a switching desk, also the movable con tact 11 will preferably be actuated from that place. This may be achieved by providing an electro-magnetic mechanism for moving the 'said contact, the control-member thereof being arranged on the switching desk. Such simple extensions, however, are within the scope of the invention.

What is claimed is:

1. X-ray apparatus comprising in combination an X- ray tube having an anode and a pair of filaments, and a circuit arrangement for energizing the same comprising a source of bidirectional voltage having a common terminal, first and second terminals adapted to pass current only in opposite directions with respect tosaid common terminal, first conductor means connecting said common terminal to one end of each of said filaments, first and second unidirectional elements having opposite electrodes connected to the other ends of said filaments, second conductor means connected to the remaining electrodes of said first and second unidirectional elements for connecting said first and second unidirectional elements to one of said first and second terminals, and switch means to selectively connect said second conductor means to one of said first and second terminals.

2. X-ray apparatus comprising in combination an X-ray tube having an anode and a pair of filaments and a circuit arrangement for energizing the same comprising a'source of bidirectional voltage having first and second terminals and a common terminal, first conductor means connecting said common terminal to one end of each of said filaments, said source including a first pair of undirectional elements for passing current to said first and second terminals in opposite directions with respect to said common terminal, a second pair of unidirectional elements for passing current in opposite directions with respect to said common terminal connected to each of the other ends of said filaments, a second conductor means connecting said second pair of unidirectional elements to one of said first and second terminals, and switch means for selectively connecting said second conductor to one of said first and second terminals.

3. X-ray apparatus comprising in combination an X ray tube having an anode and a pair of filaments, and a circuit arrangement for energizing the same, comprising a source of bidirectional voltage for supplying voltages of dififerent magnitudes and having first and second terminals and a common terminal, first conductor means connecting said common terminal to one end of each of said filaments, a first pair of unidirectional elements for passing current in opposite directions with respect to said common terminal connected to said first and second terminals, a second pair of unidirectional elements connected to each of the other ends of said filaments for passing current in opposite directions with respect to said common terminal, a second conductor means for connecting said second pair of unidirectional elements to one of said first and second terminals, and switch means for selectively connecting said second conductor means to one of said first and second terminals.

4. X-ray apparatus comprising in combination an X- ray tube having an anode and a pair of filaments, and a circuit arrangement for energizing the same comprising a source of bidirectional voltage including a source of alternating voltage and bridge rectifying means to convert said alternating voltage into a bidirectional voltage, said source having first and second terminals to which unidirection-a1 voltages of opposite directions are supplied by said rectifying means and a common terminal, a first conductor means connecting said common terminal to one end of each of said filaments, a pair of unidirectional elements connected to the other ends of said filaments, a second conductor means connecting said pair of unidirectional elements to one of said first and second terminals, and switch means for selectively connecting said second conductor means to one of said first and second terminals.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Coolidge May 9, 1933 Suits May 30, 1939 Neimann et a1 Nov. 25, 1941 Hang et a1. June 9, 1942 6 Boldingh Oct. 12, 1954 Worden May 29, 1956 FOREIGN PATENTS Germany Mar. 5, 1938 Austria Dec. 10, 1940 France Apr. 21, 1954 

1. X-RAY APPARATUS COMPRISING IN COMBINATION AN XRAY TUBE HAVING AN ANODE AND A PAIR OF FILAMENTS, AND A CIRCUIT ARRANGEMENT FOR ENERGIZING THE SAME COMPRISING A SOURCE OF BIDIRECTIONAL VOLTAGE HAVING A COMMON TERMINAL, FIRST AND SECOND TERMINALS ADAPTED TO PASS CURRENT ONLY IN OPPOSITE DIRECTIONS WITH RESPECT TO SAID COMMON TERMINAL, FIRST CONDUCTOR MEANS CONNECTING SAID COMMON TERMINAL TO ONE END OF EACH OF SAID FILAMENTS, FIRST AND SECOND UNIDIRECTIONAL ELEMENTS HAVING OPPOSITE ELECTRODES CONNECTED TO THE OTHER ENDS OF SAID FILAMENTS, SECOND CONDUCTOR MEANS CONNECTED TO THE REMAINING ELECTRODES OF SAID FIRST AND SECOND UNIDIRECTIONAL ELEMENTS FOR CONNECTING SAID FIRST AND SECOND UNIDIRECTIONAL ELEMENTS TO ONE OF SAID FIRST AND SECOND TERMINALS, AND SWITCH MEANS TO SELECTIVELY CONNECT SAID SECOND CONDUCTOR MEANS TO ONE OF SAID FIRST AND SECOND TERMINALS. 